In an electrical communication system, it is sometimes advantageous to transmit information signals (video, audio, data) over a pair of wires (hereinafter “wire-pair” or “differential pair”) rather than a single wire, wherein the transmitted signal comprises the voltage difference between the wires without regard to the absolute voltages present. Each wire in a wire-pair is susceptible to picking up electrical noise from sources such as lightning, automobile spark plugs and radio stations to name but a few. Because this type of noise is common to both wires within a pair, the differential signal is typically not disturbed. This is a fundamental reason for having closely spaced differential pairs.
Of greater concern, however, is the electrical noise that is picked up from nearby wires or pairs of wires that may extend in the same general direction for some distances and not cancel differentially on the victim pair. This is referred to as crosstalk. Particularly, in a communication system involving networked computers, channels are formed by cascading connectors and cable segments. In such channels, the proximities and routings of the electrical wires (conductors) and contacting structures within the connectors also can produce capacitive as well as inductive couplings that generate near-end crosstalk (NEXT) (i.e., the crosstalk measured at-an input location corresponding to a source at the same location) as well as far-end crosstalk (FEXT) (i.e., the crosstalk measured at the output location corresponding to a source at the input location). Such crosstalks occurs from closely-positioned wires over a short distance. In all of the above situations, undesirable signals are present on the electrical conductors that can interfere with the information signal. As long as the same noise signal is added to each wire in the wire-pair, the voltage difference between the wires will remain about the same and differential crosstalk is not induced, while at the same time the average voltage on the two wires with respect to ground reference is elevated and common mode crosstalk is induced. On the other hand, when an opposite but equal noise signal is added to each wire in the wire pair, the voltage difference between the wires will be elevated and differential crosstalk is induced, while the average voltage on the two wires with respect to ground reference is not elevated and common mode crosstalk is not induced. The term “differential to differential crosstalk” refers to a differential source signal on one pair inducing a differential noise signal on a nearby pair. The term “differential to common mode crosstalk” refers to a differential source signal on one pair inducing a common mode noise signal on a nearby pair.
110-style cross-connect wiring systems are well known and are often seen in wiring closets terminating a large number of incoming and outgoing wiring systems. Cross-connect wiring systems commonly include index strips mounted on terminal block panels which seat individual wires from cables that connect with 110-style punch-down wire connecting blocks that are subsequently interconnected with either interconnect wires or patch cord connectors encompassing one or more pairs. A 110-style wire connecting block has a dielectric housing containing a plurality of double-ended slotted beam insulation displacement contacts (IDCs) that typically connect at one end with a plurality of wires seated on the index strip and with interconnect wires or flat beam contact portions of a patch cord connector at the opposite end.
Two types of 110-style connectors are most common. The first type is a connector in which the IDCs are generally aligned with one another in a single row (see, e.g., U.S. Pat. No. 5,733,140 to Baker, III et al., the disclosure of which is hereby incorporated herein in its entirety). The second type is a connector in which the IDCs are arranged in two rows and are staggered relative to each other (see, e.g., GP6 Plus Connecting Block, available from Panduit Corp., Tinley Park, Ill.). In either case, the pairs sequence from left to right, with each pair consisting of a positive polarized terminal designated as the “TIP” and a negatively polarized terminal designated as the “RING”,
The staggered arrangement results in lower differential to differential crosstalk levels in situations in which interconnect wires (rather than patch cord connectors) are used. In such situations, the aligned type 110-style connector relies on physical separation of its IDCs or compensation in an interconnecting patch cord connector to minimize unwanted crosstalk, while the staggered arrangement, which can have IDCs that are closer together, combats differential crosstalk by locating each IDC in one pair approximately equidistant from the two IDCs in the adjacent pair nearest to it; thus, the crosstalk experienced by the two IDCs in the adjacent pair is essentially the same, with the result that its differential crosstalk is largely canceled.
These techniques for combating crosstalk have been largely successful in deploying 110-style connectors in channels supporting signal transmission frequencies under 250 MHz. However, increased signal transmission frequencies and stricter crosstalk requirements have identified an additional problem: namely, differential to common mode crosstalk. This problem is discussed at some length in co-pending and co-assigned U.S. patent application Ser. No. 11/044,088, filed Mar. 25, 2005, the disclosure of which is hereby incorporated herein in its entirety. In essence, differential to common mode crosstalk occurs when one pair of conductors behaves as a single “phantom” conductor when another pair of conductors is differentially excited. Thus, when physical proximities of the conductors of one pair to the conductors of a second pair differ significantly, uncompensated differential to common mode crosstalk can occur. Neither of the 110-style connectors discussed above is designed to address the problem of differential to common mode crosstalk in the IDCs of the connector.